This is a special version of the Headphone adapter to mate with the UA2.5v2 amplifier, making it into either a headphone amplifier or a preamplifier. We use this in combination with the UA2.5v2 as a preamplifier for the monoblocks, and it can accommodate as many as three PAIRS of monoblocks to tri-amplify a pair of speakers. This product has hundreds of uses making it the most useful audiophile tool you never knew you needed. Basically, it is a stepped attenuator and can impedance match devices. This is a much better and has more options than the original headphone adapter.